Microscopy in gemmology is used for gemstone determination and quality control, with these devices e.g. internal proberties are visualised. In the science of gemmology, all visually recognisable irregularities within gemstones, such as material foreign bodies (minerals, liquids, gases), cracks, colour zoning or twin lamellae, are understood as inclusions. They are often not visible to the naked eye, unless a microscope is used. The type and form of the inclusions are often a good indication of which gemstones are involved and from which sources they originate. How is that possible? It has been determined that the origin and genesis of gemstones can manifest themselves in characteristic inclusions. That needs to be investigated.
The instruments can be used horizontally as well as vertically , depending on the configuration. All A.KRUSS microscopes for gemmological use are usually stereo microscopes. In addition to the usual microscope components, gemstone microscopes have stone and cuvette holders and polarisation filters. All A.KRUSS microscopes for gemmological use are usually stereo microscopes.
Function stereo microscope
The stereo microscope is a special light microscope in which a separate beam path is provided for both eyes. Both eyes therefore see the stone under examination from a slightly different angle, so that a stereo effect occurs. The human brain combines the two images into a single image with some depth. This creates an almost spatial impression, which is the reason for the name stereo (two-channel) microscope.
The most important method of stereomicroscopy: Brightfield microscopy, which is one of most adopted for the investigation of gemstones. In this way most of the inner characteristics of a gemstone can be detected. In bright-field microscopy, the stone is illuminated from below and can thus be studied microscopically by means of the transmitted light. The exampleshows zircon grains with stress cracks in ruby, found in Sri Lanka.
Function examine with immersion liquid
Gemstones are embedded in different immersion liquids to make them easier to examine under a microscope. This makes it possible to observe the stone from different angles.
A horizontal positioning of the microscope is methodologically beneficial for these investigations. The liquid causes interfering reflections of the surface or stone facets to disappear, the inclusions then appear to float in the stone or liquid. The exampleshows a composite imitation of wo stones, a garnet-glass doublet. Further practical tips can be found in the applications: Observing inclusions & determining localities .
Do you want to read more?
If you are looking for more expert information, please order the white paper “Gemstone Microscopy”. For example, this publication describes the following examination methods:
- Gemstone interior as seen through the stereo microscope
- Function and illumination with brightfield microscopy
- Function and illumination with polarisation device
- Function and illumination with dark-field microscopy
- Function and illumination incident-light device on the basis of darkfield microscopy
- Microscopy with immersion liquid
- Rubies are they natural or lab-created?
- Observing characteristic inclusions of aquamarine
- Determining the place of origin of an emerald
- Examining rubies with bright field illumination
- View rutile needles (TiO₂) in natural sapphire
The whitepaper was produced in collaboration with Prof. Dr. Jochen Schlueter wrote. He is a graduate mineralogist and responsible for the display collection of the Mineralogical Museum in Hamburg.
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